| charateristics | OR | 95%CL | P |
| Region |
|
| 0.000 |
| Eastern | reference |
|
|
| Midwestern | 0.456 | 0.379 - 0.547 |
|
| Ethnicity |
|
| 0.002 |
| Han | reference |
|
|
| Mongolian | 1.269 | 0.880 - 1.830 |
|
| Other | 2.909 | 1.555 - 5.443 |
|
| Occupation |
|
| 0.000 |
| Yes | reference |
|
|
| No | 2.089 | 1.652 - 2.640 |
|
| Education level |
|
| 0.000 |
| low | reference |
|
|
| high | 1.386 | 1.184 - 1.622 |
|